1. Field of the Invention
The present invention is broadly concerned with the improved methods and apparatus for the contact planarization of surfaces such as those developed during the manufacture of advanced integrated circuit and other devices. More particularly, the invention is concerned with such methods and apparatus wherein a coated substrate is placed adjacent an optical flat flexible sheet, and the latter is first deflected to contact a central region of the coating, followed by full, pressurized planarizing contact between the sheet and coating; during such pressurized planarizing contact, the coating is cured. Post-curing separation of the sheet and coating preferably involves generating a pressure differential between the sheet and coating which creates a smooth edge-to-center separation.
2. Description of the Prior Art
Advanced integrated circuit (IC) designs are highly dependent on increasingly complex device-layering techniques to produce semiconductor devices that are more powerful, have lower profiles, and require less energy to operate. To make these qualities possible, more circuits with much finer structures must be integrated into a microchip by constructing multiple layers of interconnects and dielectrics on a semiconductor substrate in an appropriate sequence. To construct an IC, many layers containing ultra-fine structures must be patterned onto a semiconductor surface. Currently, photolithography is the predominant technique used to pattern these ultra-fine structures. This technique requires materials to be deposited and removed from the surface to construct such ultra-fine structures.
Photolithography involves depositing a photosensitive material, known as a photoresist, onto a semiconductor substrate surface. An optical transparent object, known as the photomask or reticle, with pre-defined images of the structures to be built on the semiconductor surface is placed above the photoresist-coated substrate. An appropriate wavelength of light is illuminated through the optical object. The light either decomposes or cures the exposed area of the photoresist, depending on the nature of the photoresist and the process. The semiconductor surface is then developed to produce the patterned image on the substrate surface, and the device is ready for subsequent processing.
Materials can be applied in a uniform thickness if the surface to be coated is entirely planar. However, if the surface is not planar, that is, it has topographic features, materials may not coat with a uniform thickness, which may greatly affect the final yield or performance of the device. A coating deposited on top of a topographic surface tends to contour the topography of the underlying surface, thus producing a non-planar surface.
Fabricating one layer on top of another produces the multi-layer structure of an IC. The first layer of the structure is built on a totally planar semiconductor surface. As a result, a topographic surface is introduced onto the semiconductor substrate surface. The second layer is built on top of the topographic surface of the first structural layer. As more layers are built on the substrate, the severity of the surface topography increases. The non-planar surface is no longer suitable for constructing the next structural layer. Therefore, the topographic surface needs to be planarized, or flattened, prior to the construction of the next layer. To planarize the topographic surface, techniques such as plasma etch-back, chemical mechanical polishing (CMP), and contact planarization can be used.
The plasma etch-back technique involves the deposition of a thick film to smooth the underlying topographic surface to some extent. As the thickness of the film increases, surface planarity is improved. However, a longer plasma etch time is needed to etch the thicker films. The deposited film is required to have a matched plasma etch rate to that of the underlying topographic layer material under specific etch parameters. Subsequently, the thick film is etched in a plasma etcher to the underneath topographic layer to improve th surface planarity. This planarization technique has been used and known to those skilled in the art.
The CMP technique uses a slurry solution to mechanically polish the surface against a pad with the assistance of chemical reactions that occur between the substrate material and the slurry solution. A slurry solution containing abrasive particles and certain chemicals is dispensed on the pad surface. The topographic substrate surface is pressed against the pad. The substrate is then polished with a circular motion against the pad to remove the topography of the surface. CMP is currently used in IC fabrication. The specific requirements and processing conditions for certain materials that need to be planarized are known to those skilled in the art.
Contact planarization, in theory, provides an alternative to plasma etch-back and CMP techniques to planarize topographic surfaces the topographic surface is first deposited with a flowable planarization material. Subsequently, the surface is pressed against an optical flat surface, which allows the material to flow around the topographic structures under certain conditions. The material is then hardened by either photo-irradiation or heat to replicate the planarity of the optical flat surface onto the planarized material surface. The planarized material surface is then released from the optical flat object surface. To facilitate the separation, the optical flat object surface can be treated with a known art to lower its surface energy. This can be achieved by depositing a thin film or low surface energy material, such as a fluoropolymer or a fluorinated compound, onto the optical flat object surface. Another approach is to put a low surface energy material with comparable surface planarity, such as a disk or film, between the planarization material and optical flat object surface. Examples of low surface energy materials are Teflon® materials, fluorocarbon polymers, or the like. The planarized material surface then undergoes plasma etch to the underlying topographic layer. The planarity of the optical flat surface is transferred to the underlying topographic layer. The topographic surface is then planarized. One requirement of the planarized material is that it needs to possess a plasma etch ratio of 1 in relation to that of the underlying topographic layer material. The plasma etch parameters required to reach a 1:1 etch rate ratio are known to those skilled in the art.
U.S. Pat. No. 6,048,799 to Prybyla et al. described the use of an optical flat surface in contact with a material that can be solidified by heat or ultraviolet (UV) irradiation to planarize topographical surfaces. The Prybyla patent does not provide the details associated with reducing the technology to practice. Specifically the separation of the coated wafer from the optical flat surface and the optimal range of process parameters required to perform fully automated contact planarization are not discussed.
Blalock et al. (U.S. Pat. No. 6,062,133) describes method and apparatus for achieving a global planarization of a surface of a deformable layer of a wafer using a curable planarization material. A deformable material is deposited onto a substrate surface. This substrate is then placed in to the apparatus with the deformable material-coated surface facing toward and pressing against an optical flat object surface under certain press force and time. The deformable material is then cured while still in contact with the optical flat object surface. The planarity of the optical flat object surface is replicated to the coated substrate surface. Like the Prybyla et al. patent, this process and apparatus does not cover the separation of the coated wafer from the optical flat surface and the optimal range of process parameters required to perform fully automated contact planarization.
In U.S. Pat. No. 6,331,488 B1, Doan et al. describes a planarization process for semiconductor substrates. This process uses an optical flat surface to press against a nonplanar insulating material-coated substrate surface onto which a deformable material is coated. The deformable material is cured while still in contact with the optical flat surface. The planarity of the optical flat surface is replicated to the planarized deformable material surface. The planarized surface then undergoes the CMP process to transfer the planarity of the planarized surface to the underlying insulating layer. This patent also fails to include the process for separating the coated wafer from the optical flat surface and the optimal range of process parameters to perform contact planarization fully automated.